U.S. Geological Survey
Fact Sheet 075-98
Version 1.0

1998

The largest eruption on Earth this century occurred at Novarupta
Volcano, Alaska, in June 1912, creating Katmai Caldera and the Valley
of Ten Thousand Smokes. Volcanic ash (more than from all other
historical eruptions in Alaska combined) devastated areas hundreds of
miles away. Such massive eruptions will occur again in southern
Alaska, threatening its rapidly growing population. To protect the
public, U.S. Geological Survey (USGS) and other scientists with the
Alaska Volcano Observatory closely monitor the State's many active
volcanoes.

On the afternoon of June 6, 1912, an ominous cloud rose into the
sky above Mount Katmai on the Alaska Peninsula. The cloud quickly
reached an altitude of 20 miles, and within 4 hours, ash from a huge
volcanic eruption began to fall on the village of Kodiak, 100 miles
to the southeast. By the end of the eruption on June 9th, the ash
cloud, now thousands of miles across, shrouded southern Alaska and
western Canada, and sulfurous ash was falling on Vancouver, British
Columbia, and Seattle, Washington. The next day the cloud passed over
Virginia, and by June 17th it reached Algeria in Africa.

During the 3 days of the eruption, darkness and suffocating
conditions caused by falling ash and sulfur dioxide gas immobilized
the population of Kodiak. Sore eyes and respiratory distress were
rampant, and water became undrinkable. Radio communications were
totally disrupted, and with visibility near zero, ships couldn't
dock. Roofs in Kodiak collapsed under the weight of more than a foot
of ash, buildings were wrecked by ash avalanches that rushed down
from nearby hillslopes, and other structures burned after being
struck by lightning from the ash cloud.

Today, the blocky lava dome of Novarupta
sits in the ash-and-debris-filled volcanic crater, more than
a mile wide, created by a cataclysmic 1912 volcanic eruption
that rained ash over southern Alaska, western Canada, and
the Pacific Northwest. Snow-capped Mount Mageik, another
potentially explosive volcano in Katmai National Park, can
be seen in the background. Photo on right shows a resident
of the devastated village of Kodiak, 100 miles southeast of
Novarupta, standing in deep drifts of ash shortly after the
June 1912 eruption (courtesy National Geographic
Society)

Similar conditions prevailed elsewhere in southern Alaska, and
several villages were abandoned forever. Animal and plant life was
decimated by ash and acid rain from the eruption. Bears and other
large animals were blinded by ash and starved when large numbers of
the plants and small animals they lived on were wiped out. Millions
of dead birds that had been blinded and coated by volcanic ash
littered the ground. Aquatic organisms, such as mussels, insect
larvae, and kelp, as well as the fish that fed upon them, perished in
ash-choked shallow water. Alaska's salmon-fishing industry was
devastated, especially from 1915 to 1919, because of the starvation
and failure of many adult fish to spawn in ash-choked streams.

In 1916, a National Geographic Society expedition led by Robert
Griggs visited Mount Katmai and found a 2-mile-wide crater where its
summit had been before 1912. Nearby, the expedition discovered a
newly formed lava dome they called "Novarupta" and huge flows of
volcanic ash filling what they named the "Valley of Ten Thousand
Smokes" for the numerous plumes of steam rising from the still-hot
ground. Griggs' descriptions of these spectacular features helped
persuade President Woodrow Wilson to create Katmai National Monument
(now National Park) in 1918.

The ash fall from the cataclysmic 1912
eruption of Novarupta (large gray shaded area) dwarfs that
produced by recent eruptions of Augustine (blue area),
Redoubt (orange area), and Spurr (yellow area) Volcanoes.
Old-timers in Alaska can recall dozens of eruptions from
these and other Alaskan volcanoes. Within 500 miles of
Anchorage, several volcanoes (brown triangles) have exploded
in Novarupta-scale eruptions in the past 4,000 years. Beyond
the areas shown here, ash fall from these recent eruptions
of Augustine, Redoubt, and Spurr Volcanoes was negligible,
but ultrafine dust and sulfurous aerosols were held aloft
and transported farther by high-altitude winds. Even though
relatively small, the volcanic ash clouds from these
eruptions still resulted in airport closures and damage to
many jet aircraft. Because of the size and frequency of
eruptions and prevailing winds, Alaskan volcanoes present a
greater threat to aviation on the west coast of the United
States than do the volcanoes of the Cascade Range in the
Pacific Northwest.

In the 1950's, volcanologists discovered that the 1912 eruption
was actually from Novarupta, not Mount Katmai. Novarupta's eruption
had removed so much molten rock (magma) from beneath Mount Katmai
that it caused a cubic mile of Katmai's summit to collapse.

The chance of another Novarupta-scale eruption occurring in any
given year is small, but such cataclysmic volcanic events are certain
to happen again in Alaska. Within 500 miles of Anchorage,
volcanologists have identified at least seven deposits of volcanic
ash younger than 4,000 years that approach or exceed the volume of
ash ejected by Novarupta in 1912, including a thick layer of ash
erupted from Hayes Volcano, only 90 miles northwest of Anchorage. Of
the numerous volcanoes scattered across southern Alaska, at least 10
are capable of exploding in a 1912-scale eruption.

In the 1950's, volcanologists discovered
that the great Alaskan eruption of 1912 was not from Mount
Katmai, as previously thought, but from a new vent at
Novarupta. The eruption removed so much molten rock (magma)
from beneath Mount Katmai, however, that a cubic mile of
Katmai's summit collapsed to form a 2-mile-wide volcanic
depression, called a caldera, which now holds a lake 800
feet deep. Nearby Trident Volcano issued several lava flows
(red) and small ash clouds during the decade beginning in
1953. There is no historical record of eruptions at Mageik,
Martin, and Griggs Volcanoes, but their vigorous sulfur-rich
fumaroles (volcanic gas vents) suggest that they might erupt
in the near future.

When volcanoes erupt explosively, high-speed flows of hot ash
(pyroclastic flows) and landslides can devastate areas 10 or more
miles away, and huge mudflows of volcanic ash and debris (lahars) can
inundate valleys more than 50 miles downstream. Around island
volcanoes, like Augustine in Cook Inlet, pyroclastic flows and
landslides can generate giant ocean waves (tsunamis) that threaten
nearby coastal communities. Explosive eruptions can also produce
large earthquakes. In 1912, when Novarupta exploded and Mount Katmai
collapsed, 14 quakes of magnitude 6 to 7 rocked the region, and
countless smaller shocks occurred. As with Novarupta, however, the
greatest hazard posed by eruptions of most Alaskan volcanoes is
airborne ash&emdash;even minor amounts of ash can cause the engines
of jet aircraft to suddenly fail in flight, create health problems,
close roads and airports, disrupt utilities, and contaminate water
supplies for hundreds of miles downwind.

In 1912, Alaska was very sparsely populated, and there were few
airplanes. Now, nearly three-quarters of a million people live in the
State, and aircraft carrying more than 15,000 passengers and millions
of dollars in cargo pass near Alaska's more than 40 historically
active volcanoes each day.

The heavy ash fall produced by a Novarupta-scale eruption
occurring today in southern Alaska would bring the State's economy to
a standstill and kill or injure hundreds. Clinics would be
overwhelmed by people with eye, throat, and lung damage. Building
ventilation systems would have to be closed to outside air. Ash
entering computers, bankcard machines, and other electronic equipment
would cause them to break down. Automobile, snowmobile, and boat
engines would also be damaged. Airports, including Anchorage, which
handles the largest amount of air cargo of any airport in the United
States and is a refueling stop for many trans-Pacific flights, would
be closed until runways could be cleared of ash. To avoid the ash
cloud, aircraft would have to be diverted around most of Alaska,
Canada, and the Northern United States, seriously disrupting national
and international commerce.

The 1912 eruption of Novarupta was the
largest on Earth this century. Explosive eruptions are best
compared by recalculating the amount of erupted volcanic
materials, such as ash and pumice, in terms of the original
volume of molten rock (magma) released (shown
diagramatically by orange spheres). On this basis, the 3
cubic miles of magma erupted from Novarupta in 1912 was 600
times greater than the total erupted by Redoubt Volcano in
1989&endash;90 and 30 times greater than the volume of magma
released in the 1980 eruption of Mount St. Helens, which
killed 57 people and caused damage exceeding 1 billion
dollars. Even the 1991 eruption of Mount Pinatubo, the
second largest in the world this century, was less than half
the size of Novarupta's eruption.

Even years later, volcanic ash deposited within 200 miles of the
site of the eruption would be remobilized by windstorms and blown
high into the atmosphere, renewing the hazards for people and
machinery. Fish and wildlife would be devastated as they were after
the 1912 eruption, wreaking prolonged havoc on Alaska's now large and
economically important fishing and tourism industries.

Promptly restoring normal life would depend heavily on community
spirit, civic organization, and pre-eruption planning. By working
closely with local authorities, air carriers, and the public, the
Alaska Volcano Observatory (AVO), a cooperative effort of the U.S.
Geological Survey (USGS), the University of Alaska Fairbanks
Geophysical Institute, and the Alaska Division of Geological and
Geophysical Surveys, is helping to minimize the effects of volcanic
eruptions on Alaskan communities. AVO provides volcano hazards
assessments and closely monitors the State's volcanoes for any signs
of unrest, so that it can issue timely warnings of impending
eruptions.

In addition to active participation in AVO, the ongoing work of
the USGS Volcano Hazards Program in other volcanically active regions
of the United States, including Hawaii, California, Arizona, Wyoming,
and the Pacific Northwest, is helping to better protect people's
lives and property from volcano hazards.

COOPERATING ORGANIZATIONS
Alaska Division of Geological and Geophysical Surveys
Geophysical Institute, University of Alaska Fairbanks
Federal Aviation Administration
National Geographic Society
National Park Service
National Weather Service